The copying and redistribution of audio productions has long been a cause of lost revenues to the creators/producers of such material. The advance of technology has not only expanded the means of legitimate distribution for audio works, but has also made it easier to copy these materials for unauthorized purposes.
Various methods have been developed to eliminate or limit both sophisticated and unsophisticated illegitimate distribution. Some of these methods rely on physical means. Others employ a “don't copy” signal to disable a machine's recording function.
In accordance with preferred embodiments of the present invention, a multi-bit control message (sometimes termed a “digital watermark”) is embedded directly into the an audio signal, or the brightness levels of a still image. Hardware or software systems can then read this control message and, for example, disable recording functions if so instructed.
Key practical issues are addressed whereby the perceptual impact of this added message can be adjusted—both overall and as a function of the underlying visual content. For example, a blank video sequence ought in general to have minimal visible effects, whereas active motion scenes with various areas of high detail can generally tolerate more visual energy in a watermark.
Methods are further detailed whereby the embedded message can survive lossy compression processes. An example of a lossy compression process is the MPEG video compression standard. (MPEG is commonly employed when video is distributed in digital form, e.g. on optically encoded disks.)